Kotlin vs Java: a detailed
comparison & typical use cases

In Java, common development operations require explicit instructions and repetitive boilerplate, resulting in verbose code that makes development and maintenance time-consuming and more prone to errors. However, recent additions of modern features to Java help reduce verbosity, simplify certain coding patterns, and make Java codebases easier to maintain.

With Kotlin simplifying common coding patterns, developers can write fewer lines of code than in Java to achieve the same functionality. Kotlin’s features like extension functions, data classes, type inference, and smart casts allow for automatic completion of routine coding tasks, reducing repetitive work and leading to faster development and time-to-market.

While Java can call Kotlin code and use its libraries, some Kotlin-specific features that Java does not inherently support can be only partially accessible or require adaptations and workarounds.

Kotlin allows developers to use Java classes, methods, and fields directly within Kotlin code without conversion or extensive modification. Kotlin integrates seamlessly with Java libraries and existing Java codebases, meaning both languages can be used simultaneously within the same application. This compatibility is particularly beneficial for companies migrating Java applications to Kotlin as it allows for gradual adoption of the new language without the need to rewrite the entire codebase at once.

Both Java and Kotlin code compile into the same kind of bytecode that runs on the Java Virtual Machine (JVM). That’s why applications built with both languages demonstrate similar runtime performance. Java is generally preferred over Kotlin for devices with limited hardware resources, such as POS terminals, due to its mature support for embedded JVM environments and smaller runtime footprint. However, since Kotlin provides additional features, such as null safety, type inference, and additional checks, its compilation time can slightly increase due to the extra processing the Kotlin compiler performs, especially in large projects.

In addition, both languages support data-oriented programming that helps developers ensure efficient organization and processing of data, leading to faster data retrieval, reduced latency, and overall smoother app performance, especially in data-intensive or real-time applications.

Java has a mature and well-established ecosystem, offering a wide range of libraries, frameworks, plugins, and developer tools, that enables developers to utilize proven, time-tested solutions to quickly build and maintain robust, reliable applications.

Kotlin developers can seamlessly use the same tooling available to Java developers, including integrated development environments (IDEs), build tools, and testing frameworks. In addition, Kotlin offers a range of dedicated frameworks and tools, such as Ktor, Jetpack Compose, and Kotlin Multiplatform, designed to fully leverage Kotlin’s unique features, reflecting a maturing ecosystem characterized by strong community support and continuous innovation.

Java can be easy to master for developers already familiar with another programming language (like Scala or Python) as Java uses many universal programming fundamentals. However, Java’s verbose syntax makes the learning curve steeper for complete beginners, requiring them to understand and write more code for common tasks. Still, the well-established documentation, extensive learning resources, and community support help developers overcome the initial complexity and become proficient over time.

Kotlin’s concise syntax makes it easier to learn for Java specialists. However, Kotlin’s heavy reliance on the Java ecosystem and the need to understand the interoperability concepts adds complexity and demands extra learning effort from developers, especially beginners.

Java is positioned as the third most used programming language in the Stack Overflow ranking. It’s also among the top 3 languages by the tutorial searches in the PYPL Index. Companies have high demand for Java specialists, with 39% of recruiters looking to hire developers with Java skills, which makes it the third most sought language according to CoderPad.

Kotlin is officially the preferred language for Android development, with 60% of Android developers building apps using Kotlin. However, it seems to be less popular than Java in general. Kotlin ranks among the 15 most popular languages by the number of developers using it (Stack Overflow), by the tutorial searches in the PYPL Index, and by the number of companies searching for Kotlin specialists (CoderPad). This means that the Kotlin talent pool can be smaller than for the more established language like Java, so companies requiring experienced Kotlin developers can face recruitment challenges, particularly for projects beyond Android development.